Research On The Preparation And Energy Storage Performance Of Nitrogen-doped Carbon And Niobium Pentoxide Composites

As a kind of important functional materials,niobium pentoxide?Nb₂O₅?has important application in the field of energy storage.On the one hand,Nb₂O₅shows great ion intercalation/deintercalation properties and surface pseudocapacitive reaction.On the other hand,Nb₂O₅has been tested to be more sulfophilic,which can capture more polysulfide?Li PSs?and accelerate conversion dynamics of Li PSs as a catalyst,thereby limiting the shuttle effect of polysulfide to promote lithium-sulfur batteries performance.Therefore,the applications of Nb₂O₅in lithium/sodium ion hybrid capacitors and lithium-sulfur batteries have been extensive researched.Particularly,in sodium ion hybrid capacitors,orthogonal Nb₂O₅with larger?001?interplanar lattice spacing and typical pseudocapacitance,realize high energy and high power density simultaneously.However,poor electrical conductivity of the Nb₂O₅seriously hampers its potential applications in sodium-ion hybrid capacitors and lithium-sulfur batteries.In view of the poor conductivity of Nb₂O₅,this work trying to improve the electrical conductivity of Nb₂O₅by combining with nitrogen doped carbon,and explore the application of composite materials in sodium ion hybrid capacitors and lithium-sulfur batteries.The main research results are as follows:?1?A novel composite of Nb₂O₅and nitrogen doped carbon?NC@Nb₂O₅?was prepared via hydrolysis reaction of niobium pentachloride and following thermal annealing using the two-dimensional g-C₃N₄as the template.The prepared composite has a reversible capacity of 266 m A h g^-1at current density of 0.05 A g^-1,and capacity retention rate of 90.3%for a large current density of 1 A g^-1after 1000 times.The electrochemical kinetics shows that the composite has remarkable pseudocapacitive charge storage characteristic.The sodium-ion hybrid capacitors were assembled by using the NC@Nb₂O₅composite as the negative electrode and activated carbon as the positive electrode.The electrochemical performance tests show that the sodium ion hybrid capacitor deliver an energy density/power density of 12 W h kg^-1/15302 W kg^-1under the voltage window of 0.01-3 V and has the coulomb efficiency beyond 99%after 1000 cycles.The results indicate that the NC@Nb₂O₅composite has important application in high performance sodium-ion hybrid capacitors.?2?By adjusting the content of two-dimensional g-C₃N₄,the NC@Nb₂O₅composite with high carbon content was prepared.Then the NC@Nb₂O₅composite is used to modify commercial polypropylene separator by vacuum fabricating to obtain functional separator for lithium-sulfur batteries.Compared with the commercial polypropylene separator,the modified separator by the NC@Nb₂O₅composite can significantly improve the performance of the lithium-sulfur batteries.The specific capacity of the lithium sulfur batteries with the modified separator is up to 693 m A h g^-1at 3 A g^-1.Further research shows that the improvement of the electrochemical performance for lithium-sulfur batteries is due to the efficient adsorption and catalytic transformation of lithium polysulfide by the modified separator with the NC@Nb₂O₅composite material,thereby improving the utilization of sulfur active materials.